The present invention relates to method and apparatus for producing a plurality of sets of copies of a mlulti-sheet document each time the sheets of the document are circulated seriatim to an exposure position.
U.S. Pat. No. 4,176,945, which issued on Dec. 4, 1979 in the names of R. C. Holzhauser et al, discloses a copier/duplicator with a recirculating feeder for receiving a set of document sheets and circulating the document sheets seriatim to a platen. A document sheet at the platen is illuminated to form a latent image of a page of the document sheet on a photoconductor. The latent image is developed, transferred to a copy sheet and fused to the copy sheet to form a copy of the page of the document sheet. Document sheets fed by the recirculating feeder can be either simplex document sheets or duplex document sheets. A simplex document sheet has information to be copied only on one side or face of the document sheet, and a duplex document sheet has information to be copied on both sides or faces of the document sheet. When duplex document sheets are to be copied, the copier duplicator forms on the photoconductor two adjacent latent images of opposite sides of the duplex document sheet. The latent images are developed. One such developed image is transferred to one side of the copy sheet and then the copy sheet is inverted and the second developed image is immediately transferred to the second side of the copy sheet. After fusing, the copy sheets are stacked in the same order as the document sheets in the feeder. Such apparatus has proved to be successful for forming one set of copy sheets each time a set of document sheets is circulated seriatim to an exposure platen for illumination and copying.
A copier/duplicator as described above is quite desireable because the copies produced can be collected in a tray with the copy sets arranged in the same page sequence as the pages of the original document. Such eliminates the need for a collator as an accessory to the copier/duplicator. However, the sheets of the document normally are circulated to the platen at the same rate copies are produced by the copier/duplicator. Copier/duplicators may produce copies at high rates, e.g., approximately 4,000 to 8,000 copies per hour. Thus very little time is available for removing one page of a document sheet from a platen, then feeding a second page of the document sheet or a second sheet to the platen and registering it for copying without reducing the maximum rate of copying of the copier/duplicator. The need to circulate document sheets in a recirculating feeder at rates equal to the high rates copies are produced increases the possibility that document sheets may be damaged, misfeeding of sheets may occur, sheets are not properly registered for copying, etc. Thus the need to circulate the document sheets at high rates can be a difficult problem and may limit the maximum rate at which copies can be produced by a copier/duplicator when document sheets are being handled by a recirculating feeder.